This is replication with a middle class sample of 49 infants of a study previously carried out with a sample composed largely of lower socioeconomic infants and families. Data on environmental variables are obtained through timesampling observations in the homes. Measures of infant development are obtained from the Bayley Scales and through a structured test designed to measure exploratory behavior and preference for novel stimuli. In the earlier study significant relationships were found between specific environmental variables and specific aspects of infant development at 6 months. For example, kinesthetic stimulation by the mother was significantly related to the Bayley Mental Development Index and to measures of Goal Directedness, Object Permanence and Social Responsiveness. Analyses indicate that there are a variety of differences in maternal handling of infants in these socioeconomic groups, that infants in this sample received stimulation in amounts greater than the median value in the other sample. We found that in general the relationships between environmental variables and infant functioning were not replicated in the middle socioeconomic sample. These findings suggest that variations in stimulation above a certain level do not have significant impact in the first half year. BIBLIOGRAPHIC REFERENCE: Yarrow, L. J., Pedersen, F. A. and Rubenstein, J. L. Mother-infant interaction and development in infancy. In Leiderman, P. H. and Tulkin, S. (Eds.) Cultural and social influences in infancy and early childhood. New York: Academic Press, 1977.